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O Level Chemistry: Moles and stoichiometry, questions with answers

Practise 74 real questions on Moles and stoichiometry from 2021 to 2026. See the answer and explanation as soon as you answer.

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74real questions
60multiple choice
11exam sessions

About Moles and stoichiometry in O Level Chemistry

Moles and stoichiometry is one of the 12 main topics in our O Level Chemistry (Cambridge (CAIE) 5070) question bank, and about 12% of its real questions come from it. Tayyari Karo has 74 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2, Paper 3, Paper 4; 60 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 69 medium, 4 hard, 1 easy.

Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.

Try 6 real questions

These are real past-paper questions. Think of your answer first, then open the explanation.

May/June 2026 · Paper 1 · Moles and stoichiometry

Which definition of the empirical formula of a compound is correct?

  1. the number and type of different atoms or ions in one mole of the compound
  2. the number of different atoms or ions in one mole of the compound
  3. the relative number of bonds between the different atoms or ions in the compound
  4. the simplest whole number ratio of the different atoms or ions in the compound
Show answer and explanation

Answer: D. the simplest whole number ratio of the different atoms or ions in the compound

The empirical formula is the simplest whole-number ratio of the atoms (or ions) of each element in the compound.

May/June 2025 · Paper 1 · Moles and stoichiometry

Potassium oxide?

  1. KO
  2. K2O
  3. KO2
  4. K2O2
Show answer and explanation

Answer: B. K2O

K2O.

Oct/Nov 2024 · Paper 1 · Moles and stoichiometry

Formula of potassium chloride?

  1. KCl
  2. KCl2
  3. K2Cl
  4. K(Cl)2
Show answer and explanation

Answer: A. KCl

K+ + Cl- -> KCl.

May/June 2023 · Paper 1 · Moles and stoichiometry

Empirical formula of C₂H₄?

  1. CH₂
  2. C₂H₄
  3. CH
  4. C₄H₈
Show answer and explanation

Answer: A. CH₂

Divide by 2 → CH₂.

May/June 2022 · Paper 1 · Moles and stoichiometry

Mass of 0.5 mol CaCO₃? (Mᵣ = 100)

  1. 50 g
  2. 100 g
  3. 200 g
  4. 25 g
Show answer and explanation

Answer: A. 50 g

0.5 × 100 = 50 g.

May/June 2021 · Paper 1 · Moles and stoichiometry

8.00 g CaO reacts with excess HNO₃ to give 12.65 g Ca(NO₃)₂. Percentage yield? (Ar: Ca 40, N 14, O 16, H 1)

  1. 54.0
  2. 63.2
  3. 67.1
  4. 86.8
Show answer and explanation

Answer: C. 67.1

Theoretical from 8 g CaO; 12.65/theoretical × 100 ≈ 67%.

Practise all 74 Moles and stoichiometry questions

Sessions with Moles and stoichiometry questions

SessionPaper 1Paper 2Paper 3Paper 4
May/June 202641––
May/June 20256–11
Oct/Nov 20254–––
May/June 20246–––
Oct/Nov 20246–11
May/June 20235–––
Oct/Nov 20236–––
May/June 20226–11
Oct/Nov 20226–11
May/June 20215–12
Oct/Nov 20216–11

Common questions

What does the Moles and stoichiometry topic cover on this page?

74 real O Level Chemistry (5070) questions on Moles and stoichiometry from 2021 to 2026, from Paper 1, Paper 2, Paper 3, Paper 4. Each one shows the year, session and paper it came from.

Do I get the answers and explanations?

Yes. Every question shows the correct answer and a short explanation the moment you answer.

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